The US military will formally end its ban on women serving in front-line combat roles, officials said on Wednesday, in a move that could open thousands of fighting jobs to female service members.

The move knocks down another societal barrier, after the Pentagon scrapped its "Don't Ask, Don't Tell" ban in 2011 on gays and lesbians serving openly in the military.

The decision by outgoing Defense Secretary Leon Panetta is expected to be formally announced on Thursday and comes after 11 years of non-stop war that has seen dozens of women killed in Iraq and Afghanistan.

They have represented around 2 percent of the casualties of those unpopular, costly wars, and some 12 percent of those deployed for the war effort, in which there were often no clearly defined front lines, and where deadly guerrilla tactics have included roadside bombs that kill and maim indiscriminately.

"This is an historic step for equality and for recognizing the role women have, and will continue to play, in the defense of our nation," said Democratic Senator Patty Murray from Washington, the outgoing head of the Senate Veterans Affairs Committee.

The move was also welcomed by Democratic Senator Carl Levin of Michigan, the head of the Senate Armed Services Committee, who said it reflected the "reality of 21st century military operations." In addition, the American Civil Liberties Union, which filed a suit in November seeking to force the Pentagon to end the ban, applauded the move.

The decision overturns a 1994 policy that prevents women from serving in small front-line combat units.

HISTORIC MOMENT

Following the expected announcement on Thursday, the military services will have until May 15 to submit a plan for implementing the decision. That plan, which has to be approved by the defense secretary and notified to Congress, will guide how quickly the new combat jobs open up and whether the services will seek an exemption to keep some closed.

The policy would be implemented by 2016.

Anu Bhagwati, a former Marine captain and head of the Service Women's Action Network, said her decision to leave the Marine Corps in 2004 owed partly to the combat exclusion policy.

"I know countless women whose careers have been stunted by combat exclusion in all the branches," said Bhagwati, who called the decision an "historic moment."

"I didn't expect it to come so soon," she said.

For Panetta, the decision adds to his legacy as a secretary who oversaw the end of "Don't Ask, Don't Tell"